A ‘Substantial’ Atmospheric River Will Soak the West Coast This Week

Another atmospheric river will arrive in the northwestern United States on Tuesday, bringing excessive rain and mountain snow down the entire West Coast as it drifts south through Thursday.

A plume of deep moisture that will move into Northern California on Wednesday and into Southern California on Thursday has the potential to bring excessive rain that could lead to flash flooding. Forecasters with the Weather Prediction Center are already highlighting potential risk areas for Wednesday and Thursday, including northern portions of the San Francisco Bay Area on Wednesday and Los Angeles on Thursday.

California hasn’t been hit with the same level of atmospheric rivers this season as it did last year, when the state experienced the longest stretch of continuous atmospheric river conditions in the 70 years that records have been collected on these events. With nine back-to-back atmospheric rivers from December 2022 through January 2023, farmlands turned into lakes and snow piled up well above homes in the Sierra.

This midweek storm is expected to be moderate in intensity, but another possible storm on the heels of this one could escalate the situation.

“We could very well receive February’s total normal precipitation within the month’s first five days,” forecasters from the National Weather Service’s office in San Diego wrote early Monday morning.

Here’s what to know about the timing.

• Monday: A much weaker atmospheric river makes landfall in British Columbia, and some rain falls in the Pacific Northwest.

• Tuesday: The more robust storm, which forecasters in Seattle have called “a more substantial atmospheric river system,” arrives late in the Pacific Northwest. With recent heavy rains, stream and river flooding are possible.

• Wednesday: The main stream of heavy precipitation is pointed at Northern California. The worst conditions are expected from the northern Bay Area to the Oregan-California border.

• Thursday: The bulk of heavy precipitation drifts south into the Los Angeles region, with rainfall arriving in Southern California later in the day.

The slower the storm moves, the more precipitation will fall. As of Monday morning, forecasters believe it will be a quicker-moving storm, easing some of the rain totals that could pile up and lowering the potential risk for flash flooding.

In the beginning, this will be a warmer storm, confining snow levels to higher elevations, but colder air will return as the storm moves through.

There is high confidence that the Sierra will receive over a foot of snow with this storm. The highest peaks are likely to get even three times that amount.

Next week’s storm

Another storm could hit California late this weekend into next week. But there is significant uncertainty on its potential impact this far out.